Short-time scale variation of phytoplankton succession in Lisbon bay (Portugal) as revealed by microscopy cell counts and HPLC pigment analysis

The phytoplankton distribution and composition in Lisbon bay was studied, at a short time scale based on a weekly sampling, during one year (April 2004 – May 2005), using microscopic examination and pigment analysis with high-performance liquid chromatography (HPLC). This work is a contribution to the knowledge on species succession and ecology of coastal communities. The frequency of the sampling permitted monitoring peak blooming and decaying, a process which frequently occurred within 1 –2 weeks. Cell counts determined that the classes Dinophyceae, Bacillariophyceae and Prymnesiophyceae dominated the assemblages. Maxima abundances and diversity of phytoplankton were observed from spring to autumn. HPLC analysis reflected the major seasonal variations observed by the cell counts and in addition detected the presence of four small sized phytoplankton classes that were not identified by microscopy. Phytoplankton counts were essential to identify the main contributing species to total chlorophyll a. Fucoxantin, peridinin and 190-hexanoyloxyfucoxanthin appeared as good indicators for diatoms, dinoflagellates and coccolithophores, respectively, with synchronized seasonal variations and significant positive correlations.